In most brain surgery it is necessary to open a large hole in the skull. The opening is typically made by forming two burr holes an inch or more apart, inserting a power cutting tool into one of the holes and making about a two inch diameter semicircular cut connecting the two burr holes together, and thereby forming a resulting flap of bone (skull). The skull flap is then bent out of the way, or broken out. After the brain operation the skull flap must be replaced and held in position until the skull heals. This is typically accomplished by drilling small pairs of holes in several places around the edge of the flap in the skull. Wire is then carefully threaded through the holes taking care not to tear the dural tissue covering the brain. The wires are then twisted together to secure the edges and the ends tucked into the cut opening so that they do not puncture the skin, which is then stitched into place over the skull flap. The procedure is long and involved and there always is the possibility of injuring the dura either by using the high speed drills that are necessary to form the small holes into which the wires is placed, or by the sharp points of the wire engaging the dura.
According to the present invention a method of holding a flap of skull in place after bone surgery is provided which minimizes the possibility of injury to the dura, and also cuts down the time of the skull flap affixing procedure (compared to the typical prior art procedure described above) by about twenty to thirty minutes. The invention also relates to a craniotomy pin which is utilized in practicing the method of the invention. The craniotomy pin (preferably at least three such pins being used) holds the skull flap in place with respect to the surrounding skull in a positive manner, can easily be covered by skin during the healing process, and is simple and easy to make and use.
According to one aspect of the present invention there is provided a method of holding a flap of skull in place after brain surgery, the flap of skull being separated from the surrounding skull by an elongated opening having first and second side edges spaced apart a distance X, using at least one craniotomy pin having a head with dimensions larger than X, and a locking portion having at least two cutting edges spaced a width greater than X and having a minor part with a dimension less than X, the cutting edges being spaced from the head a distance less than the thickness of the skull. The method comprises the steps of: (a) inserting the minor part of the pin into the opening, until the head substantially abuts the skull; and (b) twisting the head of the pin so as to cause the cutting edges to cut into the skull, one cutting edge cutting into the flap of skull and another cutting edge cutting into the surrounding skull, so as to lock the locking portion in place in the skull with the head engaging the top of the skull.
Step (b) may be practiced by twisting the head in a first direction, and there are the further steps, after step (b), of (c) allowing the skull to heal, and then (d) twisting the head of the pin in a second direction, opposite the first direction, to release the cutting edges from the skull, and then removing the pin from the skull. The head preferably has reverse cuts and is devoid of slots, sockets, or other openings which can collect bacteria. Steps (b) and (d) are practiced by gripping the head at the reverse cuts with the tool, and twisting the tool. Steps (a) and (b) are preferably practiced at at least three spaced locations along the elongated opening, to positively hold the skull flap in place with respect to the surrounding skull.
According to another aspect of the present invention a craniotomy pin is provided, comprising the following elements: A head having first and second longitudinal dimensions. A locking portion having first and second spaced cutting edges and having third and fourth longitudinal dimensions, at least the third longitudinal dimension being significantly less than the first dimension. And the head and the locking portion made of sterilizable biocompatible rigid material, the cutting edges capable of cutting into a human skull, to lock in the skull.
The fourth dimension is about 3 mm or less (e.g. 2 mm), and less than the second dimension. The head is devoid of slots, sockets, or other openings which can collect bacteria and includes a reverse cuts that are substantially parallel to each other and extend in the first dimension. In fact the head comprises first and second edges extending generally along the first dimension in which the reverse cuts are formed and third and fourth edges extending generally along the second dimension, the first dimension being longer than the second dimension, and the first through fourth edges all being curved. The locking portion cutting edges and the head are spaced from each other less than the thickness of a human skull, typically about 3.5 mm or less (e.g. typically a shaft extends between the head and the locking portion, and the head, shaft and locking portion are integral and made of titanium or carbon reinforced plastic) and typically have an angle of about 40-50 degrees (e.g. about 45 degrees) with respect to the second dimension.
According to another aspect of the present invention a craniotomy pin comprising an integral construction of biocompatible rigid material is provided which includes: A head comprising a first spherical segment having side reverse cut edges, and devoid of openings which can collect bacteria. A locking portion comprising a second spherical segment, having a sphere diameter less than that of the first spherical segment and a spherical extent less than that of the first spherical segment with sharp side edges and corners. And a shaft connecting the head and locking portion, the shaft having a length of about 3.5 mm or less.
It is the primary object of the present invention to provide simple and easy to construct and utilize a craniotomy pin, and method of holding a flap of skull in place after brain surgery using one or more such pins. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended.